UPDATE: Sega has told Eurogamer that it isn't in a position to comment on who might be responsible, explaining its "internal investigation is ongoing".
A spokesperson for the publisher also said it will bring Sega Pass back online "as soon as we can" and that it intends to take all necessary measures to protect against future security breaches.
"We take the security of our customers data very seriously and constantly review our security measures. The protection of data is an evolving process, as new defences are created so new threats emerge. We will make all improvements necessary as a result of this intrusion."
ORIGINAL STORY: Sega is the latest publisher to fall foul of hackers.
Earlier today it sent out an email to all members of its Sega Pass forums announcing that it had detected an "unauthorised entry" into its database in the last 24 hours and taken the service offline.
"We immediately took the appropriate action to protect our consumers' data and isolate the location of the breach," read the statement. "We have launched an investigation into the extent of the breach of our public systems.
"We have identified that a subset of Sega Pass members emails addresses, dates of birth and encrypted passwords were obtained. To stress, none of the passwords obtained were stored in plain text.
"Please note that no personal payment information was stored by Sega as we use external payment providers, meaning your payment details were not at risk from this intrusion."
It has reset all passwords and recommended that if you use the same login information for other websites that you change it immediately.
It also asks users not to attempt to log-in to the forums until it has sent out notification that the service is back online.
"We sincerely apologise for this incident and regret any inconvenience caused."
Might LulzSec have struck again? The hacking group responsible for recent attacks on Sony Pictures, Bethesda, Nintendo and CCP, hadn't mentioned it on its Twitter feed at the time of writing.
We've contacted Sega for more information and will update when we hear back.